Double indicator pulmonary edema measurement

Abstract

Patient monitoring method and apparatus for measurement of in vivo extra vascular lung water (pulmonary edema) and pulmonary circulatory system thermal bypass utilizing double indicator dilution with temperature and electrical conductivity modifiers. A thermal modifier is utilized for a primary indicator dilution measurement with electrical conductivity provided as a reference indicator which in turn is corrected for temperature effects produced by the thermal moderator as well as effects of plasma characteristics. Thermal and conductivity sensors are both placed upstream and downstream of the lungs in the pulmonary artery and thesystemic arterial system, and a thermal and conductivity moderator is injected at a site upstream from both. Temperature and conductivity are detected at both sites and the conductivity signal is converted to a volume dilution valve. Lung water is then determined as a function of the mean transit time difference of the two sensed temperatures less the mean transit time difference for the two conductivity based volume dilutions. Because the measurement is based on four sensors and mean transit time differences are used, in vivo error sources merely act as more signal and do not affect the final values. The detected signals are also analyzed in a manner to yield information on thermal bypass. The measurement technique disclosed is useful in correcting the effects of a conductivity indicator for thermal and blood effects however employed.

What is claimed is: 
     
       1. A method for measuring extra vascular lung water in vivo comprising the steps of: injecting a temperature and conductivity modifier into the blood circulatory system in a location whereby the modifier passes through the pulmonary vascular system;   measuring temperature and conductivity in the circulatory system downstream of the point of modifier injection including respective locations upstream and downstream of the pulmonary vascular system to provide two temperature and two conductivity measurements;   The injection of the thermal diluent causing a disturbance in the measured conductivity;   adjusting the measured conductivity as a function of at least one property other than hematocrit of blood selected from the group consisting of temperature, osmolality, red cell form factor, water content and ion dissociation factor whereby the disturbance of the thermal diluent on measured conductivity is corrected; and   determining the extra vascular lung water value from measured temperature and adjusted conductivity.   
     
     
       2. The method of claim 1 wherein said adjusting step includes providing a volume dilution value for each measured conductivity. 
     
     
       3. The method of claims 1 or 4 wherein said determining step includes determining the overall mean transit time differences for temperature and adjusted conductivity. 
     
     
       4. The method of claim 1 wherein: said injecting step includes injecting a temperature and conductivity modifier in a vena cava, ahead of the right heart;   said measuring step includes measuring temperature and conductivity in the pulmonary artery and measuring temperature and conductivity in the systemic arterial system.   
     
     
       5. The method of claim 1 wherein said injecting step includes the step of injecting a cold saline solution. 
     
     
       6. The method of claim 1 wherein: said measuring step includes the step of determining from measured temperature the volume dilution of temperature separately for the pulmonary artery and systemic arterial system;   a step is included for determining a measure of thermal bypass from the volume dilution of conductivity and temperature.   
     
     
       7. The method of claim 1 further including the step of adjusting conductivity for hematocrit. 
     
     
       8. A method for detecting thermal bypass in a circulatory system comprising the steps of: applying a modifier of temperature and conductivity to a circulatory system including a thermal mass;   detecting volume dilution values as a function of time for temperature and conductivity, at at least two separate locations in said circulatory system, one upstream and one downstream of said thermal mass, in response to the applied modifier of temperature and conductivity;   determining a measure of thermal bypass from said detected volume dilution values.   
     
     
       9. The method of claim 8 wherein said determining step includes determining the overall difference in temperature and conductive volume dilution appearance time between said separate locations. 
     
     
       10. The method of claim 8 wherein said determining step includes determining the area between the detected volume dilution values for the downstream location, with the upstream location volume dilution values adjusted into coincidence at their respective times of appearance. 
     
     
       11. Apparatus for measuring extra vascular lung water in vivo comprising: means for injecting a temperature and conductivity modifier into the blood circulatory system in a location whereby the modifier passes through the pulmonary vascular system;   means for measuring temperature and conductivity in the circulatory system downstream of the point of modifier injection including respective locations upstream and downstream of the pulmonary vascular system to provide two temperature and two conductivity measurements;   the injection of the thermal diluent causing a disturbance in the measured conductivity;   means for adjusting the measured conductivity as a function of at least one property other than hematocrit of blood selected from the group consisting of temperature, osmolality, red cell form factor, water content and ion dissociation factor whereby the disturbance of the thermal diluent on measured conductivity is corrected; and   means for determining the extra vascular lung water value from measured temperature and adjusted conductivity.   
     
     
       12. The apparatus of claim 11 wherein said adjusting means includes means for providing a volume dilution value for each measured conductivity. 
     
     
       13. The apparatus of claims 11 or 19 wherein said determining means includes means for determining the overall mean transit time differences for temperature and adjusted conductivity. 
     
     
       14. The apparatus of claim 11 wherein: said injecting means includes means for injecting a temperature and conductivity modifier in a vena cava, ahead of the right heart;   said measuring means includes means for measuring temperature and conductivity in the pulmonary artery and measuring temperature and conductivity in the systemic arterial system.   
     
     
       15. The apparatus of claim 11 wherein said injecting step includes the step of injecting a cold saline solution. 
     
     
       16. The apparatus of claim 11 wherein: said measuring means includes means for determining from measured temperature the volume dilution of temperature separately for the pulmonary artery and systemic arterial system;   means are included for determining a measure of thermal bypass from the volume dilution of conductivity and temperature.   
     
     
       17. The apparatus of claim 11 wherein said adjusting means is further adapted to adjust measured conductivity as a function of hematocrit in addition to said at least one other blood property. 
     
     
       18. Apparatus for detecting thermal bypass in a circulatory system having a thermal mass comprising: means for applying a modifier of temperature and conductivity to said circulatory system;   means for detecting volume dilution values as a function of time for temperature and conductivity, at at least two separate locations in said circulatory system, one upstream and one downstream of said thermal mass, in response to the applied modifier of temperature and conductivity;   means for determining a measure of thermal bypass from said detected volume dilution values.   
     
     
       19. The apparatus of claim 18 wherein said determining means includes means for determining the overall difference in temperature and conductivity volume dilution appearance time between said separate locations. 
     
     
       20. The apparatus of claim 18 wherein said determining step includes determining the area between the detected volume dilution values for the downstream location, with the upstream location volume dilution values adjusted into coincidence at their respective times of appearance.